Method for monitoring the forces in the mooring cable of a single-point mooring system

ABSTRACT

A system for monitoring the force in a mooring cable of a single-point mooring system and transmitting from the singlepoint mooring system to a ship moored thereto a signal related to the measured force whereby said ship can disconnect from said single-point mooring system when said signal exceeds a preset maximum value.

United States Patent [1 1 1 Sept. 18, 1973 METHOD FOR MONITORING THEFORCES IN THE MOORING CABLE OF A SINGLE-POINT MOORING SYSTEM [75]Inventor: Jan ,1. A1, The Hague, Netherlands [73] Assignee: Shell OilCompany, New York, NY.

[22] Filed: June 29, 1971 [21] App]. No.: 157,837

[30] Foreign Application Priority Data July 10, 1970 Netherlands 7010213[52] US. Cl 73/143, 114/230, 340/29 [51] Int. Cl. G011 5/10 [58] Fieldof Search 73/143, 144; 340/29,

[56] References Cited UNITED STATES PATENTS 2,142,135 H1939 Lawton..73/144x RA 0/0 TRANSMITTER TENS/ON DYNA MOMETER 2,795,136 6/1957 Matt73/144 2,617,294 11/1952 Sanders 73/144 3,614,869 10/1971 Flory et a1.114/230 X 3,290,931 12/1966 Fowkes et 31.... 73/141 A 1,848,828 3/1932Griffin 244/116 3,248,937 5/1966 Vincent 73/88.5 R X 3,330,154 7/1967Habem et al.... 73/143 3,281,781 10/1966 Milton 340/29 3,418,627 12/1968Lyons 340/29 Primary Examiner-Charles A. Ruehl Attorney-Theodore E.Bieber et al.

[57] ABSTRACT A system for monitoring the force in a mooring cable of asingle-point mooring system and transmitting from the single-pointmooring system to a ship moored thereto a signal related to the measuredforce whereby said ship can disconnect from said single-point mooringsystem when said signal exceeds a preset maximum value.

3 Claims, 1 Drawing Figure RA D/O RECEIVER Patented Sept. 18, 19733,759,094

RA 0/0 RA 0/0 TRANSMITTER RECEIVER DYNAMOMETER Jan J. Al

IN VE NTOR METHOD FOR MONITORING THE FORCES IN THE MOORING CABLE OF ASINGLE-POINT MOORING SYSTEM BACKGROUND OF THE INVENTION The inventionrelates to a method for monitoring the mooring force in the mooringcable of a single-point mooring system for the loading and unloading ofa ship and to an apparatus for carrying out this method.

Over the past decade, single-point mooring systems for the offshoremooring and loading or unloading of tankers have been put into use on alarge scale. These known systems are used both for the loading orunloading of liquids, such as crude oil or oil products, and of gasessuch as natural gas.

Single-point mooring systems of the abovementioned type are providedwith a mooring cable by means of which a ship can be moored by its bowin such a manner that the ship can freely swing about the single-pointmooring system.

Examples of these known single-point mooring system are described, forexample, in the patent specifications pertaining to applicants UnitedKingdom Pat. No. 977,451; No. 1,031,492 and No. 1,017,894. Thesingle-point mooring systems described in the lastmentioned patentspecifications are of the buoy type. It should be noted, however, thatthe invention can be applied equally well to single-point mooringsystems in which the buoy is replaced by a column supported on thebottom of the sea, which column is rigidly secured to the sea bottom.

When the ship is moored to the single-point mooring system for loadingor unloading purposes it is sometimes necessary to interrupt the loadingor unloading operation and to unfasten the ship from the single-pointmooring system because of deteriorating weather conditions. It iscustomary therefore during loading or unloading to keep a constant checkon the weather conditions (wind force, current strength, wave height).In this way it is difficult, however, to determine the exact moment todisconnect the ship. If one is too cautious, the ship is unnecessarilydisconnected from the singlepoint mooring system and lack of careentails the risk of damage being done to the ship or the single-pointmooring system. For these reasons it is desirable for more objectivefacts to be available in order to determine with greater certaintywhether, and if so when, the loading or unloading must be interruptedand the ship disconnected from the single-point mooring system. Since,moreover, the use of supertankers is steadily increasing, ships largerthan the design ship have to be moored frequently to the single-pointmooring system. Therefore, there is a growing need for qualitativerecording and/or observation of the force occurring in the mooring cablebetween ship and buoy during spells of bad weather.

BRIEF SUMMARY OF THE INVENTION The method according to the inventioncomprises measuring the mooring force, transmitting a signal from thesingle-point mooring system, which signal is a measure for the measuredmooring force, receiving the transmitted signal on the shore or onboard'the ship, and disconnecting the ship from the single-point mooringsystem when the signal received indicates that the mooring force exceedsa certain predetermined maximum value.

The signal is preferably transmitted or received over a radio link. ltwill be understood, however, that in principle it is also possible tomake use of an optical signal or a sound signal.

A single-point mooring system of the abovementioned type ischaracterized according to the invention in that the single-pointmooring system is provided with a tension dynamometer for measuring themooring force and with means coupled to the tension dynamometer forproducing a signal which is a measure for the measured mooring force.

BRIEF DESCRIPTION OF THE DRAWING The invention will now be described inmore detail with reference to the drawing showing one form of theinvention.

Let it be assumed that a ship 2 is to be moored to and to be loaded orunloaded via a single-point mooring system 1 as mentioned above. Weatherconditions being favorable (wind force, wave height, current strength),the ship 2 is fastened in the usual manner by its bow to a mooring cable3 of the single-point mooring system. A floating hose 6 is coupled tothe ship 2 and a start is made with loading or unloading liquid or gasvia the single-pointmooring system. The system shown is of the knownbuoy type, which is provided with a customary pipe length 5 and acustomary pipe swivel 4. If during loading or unloading weatherconditions deteriorate (increasing wind' force and/or wave height and/orcurrent strength) this will result in an increasing mooring force beingexerted in the mooring cable 3 of the single-point mooring system. It isdesirable to know the magnitude of the mooring force in the mooringcable 3 to be able to determine in a more objective manner whether ornot the time has come to unfasten. A tension dynamometer 7 of a typeknown per se is provided between the buoy l and the mooring cable 3, bymeans of which the mooring force acting in the mooring cable 3 can bemeasured as and when desired.

The single-point mooring system I carries equipment for, converting themeasured values of the mooring force into electric signals, as well asradio transmitting equipment capable of transmitting corresponding radiosignals to the coast or to the ship 2 moored to and single-point mooringsystem 1. The equipment is diagrammatically designated by referencenumeral 8. This equipment 8 is'coupled to the tension dynamometer 7,which is diagrammatically designated by the broken line 9. The signalstransmitted by 8 are received by means of receiving equipment 10 onboard the ship 2 (or on the shore, if desired), so that those on boardthe ship 2 (or on the shore, if desired) are constantly kept informed ofthe magnitude of the mooring force in the mooring cable 3. lf the saidmooring force exceeds a certain predetermined maximum value, thoseconcerned on board the ship 2 (or on the shore, if desired) know thatmeasures are to be taken or that the ship may have to be disconnectedfrom the single-point mooring system until conditions are againfavorable. If the signals are only received on the shore the ship willhave to be warned by another method, for example, by radio or optically,that unfastening is essential. A simpler and more effective methodconsists in arranging for the signals (diagrammatically designated by azigzag line 11) to be received direct by the moored ship 2, as

shown the figure.

To this end the mooring master, who as a matter of routine boards theship from the shore to assist in the mooring and unmooring of the shiprelative to the single-point mooring system, is provided with a specialportable wireless receiving unit 10. With the aid of this unit hereceives the signals 11 which are transmitted from the single-pointmooring system 1; a dial on the portable receiving unit shows the actualmooring force in tons. In this way the mooring master is constantly keptinformed of the magnitude of the mooring force in the mooring cable 3.As soon as this mooring force exceeds the permissible value, he may inconcert with the master of the ship 2 devise and take the measuresrequired to prevent damage to the ship and the single-point mooringsystem.

The electrical equipment on the single-point mooring system 1 ispreferably fed from a plurality of batteries present on the single-pointmooring system 1. To prevent these batteries from discharging in tooshort a time, the electrical equipment on the single-point mooringsystem 1 is preferably not constantly in operation. it is attractive,for example, to provide the mooring masters portable wireless receivingunit 10 with a transmitter by means of which a radio signal can betransmitted to the single-point mooring system 1 in order to actuate theelectrical equipment 8 on the single-point mooring system 1. Thesingle-point mooring system 1 may also be provided with a time switch(not shown), which is capable of automatically putting the electricalequipment 8 out of action after a certain period.

The method and apparatus according to the invention have the advantagethat optimum use can be made of the single-point mooring systems, andthis yields considerable savings.

It should be noted that in many single-point mooring systems the ship isfastened by its bow to the mooring system with more than one mooringcable. In this case each mooring cable should be provided with a tensiondynamometer, thus allowing the mooring master at any time to receive thesignals indicating the mooring force in each mooring cable.

I claim:

1. A method for monitoring the mooring forces in the mooring cable of asingle-point mooring system for the loading and unloading of a shipwherein said ship is moored by its bow to the single-point mooringsystem by means of a single mooring cable in such a manner that the shipcan freely swing about the single-point mooring system, said methodcomprising:

measuring the tension force in said mooring cable adjacent saidsingle-point mooring system;

supplying said measured force to said single-point mooring system;transmitting from said single-point mooring system to said ship a signalrepresenting the measured force;

receiving on said ship said transmitted signal and converting saidtransmitted signal to a usable display; and

disconnecting said ship from said single-point mooring system when saidreceived signal indicates that said measured force has exceeded a presetvalue.

2. The method of claim 1 wherein said signal is transmitted and receivedby radio.

3. The method of claim 2 wherein said transmission of the signal istriggered by the transmission of a signal to said single-point mooringsystem.

IF t 3 i I

1. A method for monitoring the mooring forces in the mooring cable of asingle-point mooring system for the loading and unloading of a shipwherein said ship is moored by its bow to the single-point mooringsystem by means of a single mooring cable in such a manner that the shipcan freely swing about the singlepoint mooring system, said methodcomprising: measuring the tension force in said mooring cable adjacentsaid single-point mooring system; supplying said measured force to saidsingle-point mooring system; transmitting from said single-point mooringsystem to said ship a signal representing the measured force; receivingon said ship said transmitted signal and converting said transmittedsignal to a usable display; and disconnecting said ship from saidsingle-point mooring system when said received signal indicates thatsaid measured force has exceeded a preset value.
 2. The method of claim1 wherein said signal is transmitted and received by radio.
 3. Themethod of claim 2 wherein said transmission of the signal is triggeredby the transmission of a signal to said single-point mooring system.